The IEEE 1394-1995 standard, “1394 Standard For A High Performance Serial Bus,” is an international standard for implementing an inexpensive high-speed serial bus architecture which supports both asynchronous and isochronous format data transfers. In addition, the IEEE 1394-1995 bus has a universal clock called the cycle timer. This clock is synchronized on all nodes. Isochronous data transfers are real-time transfers which take place based on the universal clock such that the time intervals between significant instances have the same duration at both the transmitting and receiving applications. Each packet of data transferred isochronously is transferred in its own time period. An example of an ideal application for the transfer of data isochronously would be from a video recorder to a television set. The video recorder records images and sounds and saves the data in discrete chunks or packets. The video recorder then transfers each packet, representing the image and sound recorded over a limited time period, during that time period, for display by the television set. The IEEE 1394-1995 standard bus architecture provides multiple independent channels for isochronous data transfer between applications. A six bit channel number is broadcast with the data to ensure reception by the appropriate application. This allows multiple applications to simultaneously transmit isochronous data across the bus structure. Asynchronous transfers are traditional reliable data transfer operations which take place as soon as arbitration is won and transfer a maximum amount of data from a source to a destination.
The IEEE 1394-1995 standard provides a high-speed serial bus for interconnecting digital devices thereby providing a universal I/O connection. The IEEE 1394-1995 standard defines a digital interface for the application thereby eliminating the need for an application to convert digital data to analog data before it is transmitted across the bus. Correspondingly, a receiving application will receive digital data from the bus, not analog data, and will therefore not be required to convert analog data to digital data. The cable required by the IEEE 1394-1995 standard is very thin in size compared to other bulkier cables used to connect such devices in other connection schemes. Devices can be added and removed from an IEEE 1394-1995 bus while the bus is operational. If a device is so added or removed the bus will then automatically reconfigure itself for transmitting data between the then existing nodes. A node is considered a logical entity with a unique address on the bus structure. Each node provides in a standard address space, an identification ROM, a standardized set of control registers and in addition, its own address space.
The IEEE 1394-1995 standard defines a protocol as illustrated in FIG. 1. This protocol includes a serial bus management block 10 coupled to a transaction layer 12, a link layer 14 and a physical layer 16. The physical layer 16 provides the electrical and mechanical connection between a device and the IEEE 1394-1995 cable. The physical layer 16 also provides arbitration to ensure that all devices coupled to the IEEE 1394-1995 bus have arbitrated access to the bus as well as actual data transmission and reception. The link layer 14 provides data packet delivery service for both asynchronous and isochronous data packet transport. This supports both asynchronous data transport, using an acknowledgement protocol, and isochronous data transport, providing an un-acknowledged real-time guaranteed bandwidth protocol for just-in-time data delivery. The transaction layer 12 supports the commands necessary to complete asynchronous data transfers, including read, write and lock. The serial bus management block 10 contains an isochronous resource manager for managing the resources associated with isochronous data transfers. The serial bus management block 10 also provides overall configuration control of the serial bus in the form of optimizing arbitration timing, guarantee of adequate electrical power for all devices on the bus, assignment of the cycle master, assignment of isochronous channel and bandwidth resources and basic notification of errors.
The AV/C Command Set is a command set used for transactions to and from consumer audio/video equipment over an IEEE 1394-1995 serial bus. This AV/C command set makes use of the Function Control Protocol (FCP) defined by IEC-61883, the ratified international standard for the transport of audio/video command requests and responses. AV/C commands are transmitted through AV/C transactions. An AV/C transaction consists of one AV/C command frame addressed to the target node's FCP_Command register and zero or more AV/C response frames addressed to the requesting node's FCP_Response register.
Each audio/video unit or subunit can implement a subset of the AV/C command set. An unsupported command received by an audio/video unit is rejected with a not implemented response. Support for the different commands is characterized as mandatory, recommended, optional and vendor-dependent. A mandatory command is supported by any audio/video device that claims compliance with the AV/C command set and that implements the audio/video unit or subunit type for which the command is defined. An AV/C compliant device is identified by an entry within its configuration read-only memory (ROM). A recommended command is optional for an AV/C compliant device, but represents a basic functionality, such as video and audio insert modes for a VCR subunit's record command. If the device supports a unit or subunit type that has the functionality corresponding to the command, it is recommended that the command be implemented. An optional command is optional for an AV/C compliant device. Support for and interpretation of a vendor-dependent command are defined by the device vendor.
AV/C commands are grouped into four command types including control, status, inquiry and notify command types. A control command is sent by a controller to another audio/video device, the target, to instruct the target to perform an operation. A target that receives a control command will return an AV/C response frame including either a not implemented, accepted, rejected or interim response code. The target will return a not implemented response code when the target does not support the control command specified or the command is addressed to a subunit not implemented by the target. The target will return an accepted response code when the target implements the control command specified and the current state of the target permits execution of the command. The target will return a rejected response code when the target implements the control command specified but the current state of the target does not permit execution of the command. The target will return an interim response code if the control command specified is implemented by the target, but the target is unable to respond with either an accepted or rejected response code within 100 milliseconds. Unless a subsequent bus reset causes the AV/C transaction to be aborted, the target will ultimately return a response frame with an accepted or rejected response code after returning an interim response code.
A status command is sent by a controller to an audio/video device to request the current status of the target device. Status commands may be sent to either audio/video units or subunits. A target that receives a status command will return an AV/C response frame including either a not implemented, rejected, in transition or stable response code. A target will return a not implemented status response code when the target does not support the status command specified or the command is addressed to a subunit not implemented by the target. A target will return a rejected status response code when the target implements the status command specified but the target state does not permit the return of status for the command. The target will return an in transition status response code when the target implements the status command specified, but the current state of the target is in transition. The target will return a stable status response code when the target implements the status command specified and the information requested is reported in the values in the AV/C response frame.
An inquiry command is used by a controller to determine whether or not a target audio/video device supports a particular control command. A controller can reliably use inquiry commands to probe the capabilities of a target, since the target shall not modify any state nor initiate any command execution in response to an inquiry command. A target that receives an inquiry command will return an AV/C response frame including either an implemented or a not implemented response code. An implemented response code notifies the controlling node that the corresponding control command specified is implemented by the target audio/video device. A not implemented response code notifies the controlling node that the corresponding control command specified is implemented by the target audio/video device.
A notify command is used by a controller to receive notification of future changes in an audio/video device's state. Responses to a notify command will indicate the current state of the target and then, at some indeterminate time in the future, indicate the changed state of the target. A target that receives a notify command will return an immediate response frame including either a not implemented, rejected or interim response code. A target will return a not implemented response code when the target does not support the notify command specified or the command is addressed to a subunit not implemented by the target. A target will return a rejected response code when the target implements event notification for the condition specified but is not able to supply the requested information. A target will return an interim response code when the target supports the requested event notification and has accepted the notify command for any future change of state. The current state is indicated by the data returned in the response frame. At a future time, the target will then return an AV/C response frame with either a rejected or changed response code.
A traditional hard disk drive records data and plays it back according to commands received from an external controller using a protocol such as the serial bus protocol (SBP). The external controller provides command data structures to the hard disk drive which inform the hard disk drive where on the media the data is to be written, in the case of a write application, or read from, in the case of a read operation.
Use of a media storage device, such as a hard disk drive, for storing streams of audio and video data is taught in U.S. patent application Ser. No. 09/022,926, filed on Feb. 12, 1998 and entitled “MEDIA STORAGE DEVICE WITH EMBEDDED DATA FILTER FOR DYNAMICALLY PROCESSING DATA DURING READ AND WRITE OPERATIONS,” which is hereby incorporated by reference. When storing audio and video data streams on such a hard disk drive, the available capacity of the device can be quickly utilized, due to the large amounts of data included in typical audio and video data streams. If multiple traditional hard disk drives are utilized to store large streams of data, then the user must typically be responsible for management of these storage and retrieval procedures. This storage management responsibility adds complexity to operations such as record and playback and requires the user to monitor and control storage and retrieval operations.